This application is a 371 of PCT/FR92/00826 filed Aug. 28, 1992.
1. Field of the Invention
The invention relates to electrochemical batteries, especially electrochemical batteries of the so-called "reserve" type. It particularly relates to means for producing the activation of such batteries.
2. Description of the Related Art
Electrochemical batteries of the reserve type are batteries intended to be set in operation after a storage period whose duration is variable and may extend for example up to 15 years and more.
This type of battery is widely used in order to provide electrical energy in ballistic devices, for example shells, missiles, etc. However, these batteries are also of great interest in other fields, for example that of security devices.
Batteries of the reserve type provide electrical energy from the instant when they are activated. The activation of the battery consists in uniting the different elements which, conventionally, convert the chemical reaction into electrical energy.
Such an electrochemical battery may comprise one or more electrochemical cells, the number of these cells being a function of the voltage to be obtained. In operation, that is to say after activation, each cell comprises two electrodes of opposite polarities in contact with a quantity of liquid electrolyte.
Most often, the liquid electrolyte is held outside the cell in a storage reservoir until the instant of activation. The activation of the battery consists in releasing the electrolyte.
In the case for example of rockets or artillery shells, during the storage period, all the quantities of electrolyte necessary for all the cells are most often contained in a single storage reservoir. The activation of the battery consists in releasing the liquid electrolyte from the reservoir and in bringing it into the cell or different cells. This activation may be obtained by combining the effects of the strong acceleration and of the speed of rotation which appear at the start of the shot: the electrolyte is released for example by breaking a cap under the effect of the longitudinal acceleration, at the instant of firing; and the electrolyte is distributed in the cells, aided to this effect by the centrifugal force due to the rotation of the device on itself.
In structures having a single storage reservoir for several cells, a significant problem resides in the balancing, that is to say the most even distribution possible of the electrolyte between the various cells, while minimising communication between the cells. In fact, in the most common case when the electrodes are of the "bipolar electrode" type, any quantity of electrolyte contained in communication ducts between cells generates a self-consumption phenomenon of the battery, which decreases the capacity of the latter for supplying energy to the working load. Furthermore, the electrolyte contained in these ducts may generate a troublesome fluctuation of the voltages delivered by the battery.
This leads in practice to the adoption of various compromises in the production of these batteries, which make the structure more complex, without thereby completely eliminating the problem of self-consumption. Examples of production of such reserve electrochemical batteries which "can be activated on firing" are found in particular in U.S. No. Pat. 2,996,564 and in French Patent Applications No. 8,815,331 and 8,909,637.
It should be noted that the problem posed by the activation of the reserve batteries, in the case of rotating ammunition, is made still more difficult in the case when the battery is mounted in a missile or projectile, which can undergo low accelerations, for example a mortar shell. The case of the mortar shell is actually particularly difficult, because of its low possible acceleration on starting, and the absence of rotation.
Thus, the principles explained above for producing the release and distribution of the electrolyte in the cells are inapplicable. Other solutions are envisaged, which are technologically much more complex.
In fact, these more complex solutions do not yet appear to have been achieved industrially. Hitherto, the electrical supply in mortar rockets has been effected using turbine and alternator systems whose implementation is complex and expensive but which have the advantage of being in existence.
The present invention relates to electrochemical batteries, in particular of the reserve type. It particularly relates to means for producing the activation of such batteries, and is applicable equally well in the case of high or low accelerations, with or without centrifugal force. It makes it possible to bring about very rapid activation while avoiding the defects of self-consumption and of poor distribution of the electrolyte. Furthermore, the invention is well suited to economical industrial production, so much so that it may be applied in numerous domains other than those already cited, for example the electrical supply of security devices, such as extinguishers, beacons, etc.